How long do seeds of the invasive tree, Ailanthus altissima remain viable?

The non-native invasive tree, Ailanthus altissima is an increasing threat to the diversity and health of temperate forests. Female trees are prolific producers of wind-dispersed seeds. It is not known if Ailanthus seeds remain viable in natural growing conditions beyond two years. We collected Ailanthus seeds from eleven sources in fall 2010 and incubated outdoors in either mixed oak leaf litter or mineral soil (10 cm depth) for five years to assess seed viability. Each May sets of seeds were retrieved, counted and sown in a greenhouse to measure germination. Initially germination rates averaged 87%, however in year 5 (2016), germination rates of seeds incubated outdoors in oak leaf litter, fell to 1.9%, while those incubated in mineral soil averaged 75%. Germination rates of soil-incubated seeds ranged from 48 to 95% among the eleven seed sources after five years. These findings demonstrate that the common practice to eliminate Ailanthus seed sources two years prior to a timber harvest is insufficient to deplete its seed bank. We propose that managers remove seed sources at minimum of six years in advance of a scheduled timber harvest. Ideally, it would be most advantageous to incorporate removal of females Ailanthus as a routine management practice.